This invention relates in general to the manufacture of tooling for shaping sheet material into three-dimensional shapes and, more specifically, so a method for laying up plastic blocks into a configuration from which the desired tool contour can be formed by numerically controlled machining and a method of modifying such tooling.
Tools in the form of patterns, core boxes, molds or dies are customarily used in manufacturing industries to accurately produce large numbers on identical parts or products. The manufacturing tool may be a single mold or die or a pair of complementary mold members having corresponding shaping surfaces. Such molds may be used to form products from hardenable liquid materials such as by casting, injection molding or compression molding. Softened sheet materials may be formed against dies by compression molding, blow molding and vacuum forming processes. Unsoftened sheet materials may be formed over dies by stretch forming, hydroforming, drawing with draw die punch and ring assemblies, etc.
A very large number of methods have been developed to produce mold or die surfaces having very precise contours for use in these shaping methods. Large shaping surfaces are conventionally formed by machining a very large block, forming a very large metal, ceramic or plastic shape and hand finishing the shaping surfaces to the desired dimensions. These large dies are difficult to form and considerable material is wasted in the machining and finishing steps. In order to reduce the cost, handling problems and large scale machining, attempts have been made to form mold or die surfaces from stacked laminations, each of the lamina being cut out in a way that the stack will have the desired cavity, as described by Clevenger et al in U.S. Pat. No. 2,679,172 to form a female casting mold. Foam slabs are cut with a hot wire under computer control as described by DeMenthon in U.S. Pat. No. 4,675,825 and glued together to form models, molds or cores.
Weaver, in U.S. Pat. No. 5,031,483, a large number of very thin laminations are each cut under computer control so that the laminations may be stacked and aligned to produce cooperating male and female molds for use in casting glass, plastic and metal products.
While these mold forming methods are effective in the casting of liquid or nearly liquid materials, they have not been effectively applied to the manufacture of dies for reshaping solid sheet materials. In the past tooling for reshaping large metal sheets has generally been made by machining a large metal block in to the desired contour or casting the large shape from plaster or the like. The tooling often has a three-dimensional shape over which the metal is reshaped by stretch forming, hydroforming, and other methods.
Typically, Miura, in U.S. Pat. No. 5,081,861, describes a die system for pressing sheet metal in which a die mold is coated with an epoxy resin, cloth layers are bonded to the resin layer and the interior of the mold is filled with a mixture of sand and an epoxy resin. While a strong and inexpensive die is made by this method, the method requires a carefully shaped mold, so that the shape of the die cannot be conveniently changed or repaired if damaged.
Although these large dies have been effective, they are very expensive to manufacture and wasteful of material. While some are machined by numerically controlled machining techniques, there is no convenient way to check the machining program for errors prior to machining a large and expensive block of material. Also, repairing any damage that might occur to the die or modifying the die after machining is difficult and expensive. Attempts to make such dies by laminating techniques such as those described above for use in the casting industries similarly suffer from the expense of cutting a large number of laminae and difficulty in achieving a precise assembly. The final assembled die again is difficult and expensive to repair or modify.
Thus, there is a continuing need for improved methods of manufacturing dies for use in forming large sheets of material, such as in the stretch forming of large metal panels.